Oestrogen and progesterone have marked effects on the secretion of the gonadotrophins
and prolactin. During most of the oestrous or menstrual cycle the secretion of gonadotrophin
is maintained at a relatively low level by the negative feedback of oestrogen and
progesterone on the hypothalamic-pituitary system. The spontaneous ovulatory surge of
gonadotrophin is produced by a positive feedback cascade. The cascade is initiated by an
increase in the plasma concentration of oestradiol-17β which triggers a surge of luteinizing …